謙虚：けんきょ: this is a word you use about others. "She's got a very modest attitude."
謙遜：けんそん: To downplay your own skills in front of others. You don't ever say "I kenson-ed." or "He kenson-ed." or "She's really kenson-ish." Normally it's only used like : "Please don't kenson. We both know you're rad." or "He declined the offer out of modesty."